Mainframe digital supercomputers are composed of functional subsystems. These subsystems may include one or more central processing units (CPUs); central memory, which is directly addressable by the CPUs; a solid state storage device (SSD) or auxiliary cache, which is accessed through high speed data channels; and input-output subsystems.
The input/output subsystems (IOS) have been traditionally used to transfer data into and out of the supercomputer system. As such, a number of peripheral devices have been coupled to the supercomputer through the IOS subsystem. Two of the most common peripherals include magnetic tape transports and magnetic disk storage units.
In operation the IOS normalizes transactions between commercially available peripheral devices and the CPU. This permits the CPU to communicate in a standard fashion with peripheral devices, with the necessary translation being provided by the IOS subsystem. This translation activity is accomplished in two steps. First, each peripheral device, a disk drive for example, usually has circuitry which converts standard command signals into data storage or retrieval operations. This circuitry is referred to as a disk controller. Second, a channel adapter has electrical circuitry sufficient to translate high level control instructions from the IOS into the basic controller command signals necessary to perform the instruction. This type of IOS has a large buffer memory, one or more input-output processors, and communicates to the other components of the computer system through various channel interfaces.
The inclusion of SSD devices in supercomputing systems as taught by U.S. Pat. No. 4,630,230 to Sundet has placed increased demands on the performance of the IOS subsystem. The distribution of additional fast cache memory throughout the system makes the performance of the system strongly dependant on the IOS data paths and performance.